Railway track circuit



Aug. 7, 1934. T. BODDE 1,969,059.

RAILWAY TRACK CIRCUIT Filed May 15, 1951 Fla-.4.

BY MM %4/ATTORNEY l waves of the alternating current.

Patented Aug. 7, 1934 UNITED STATES RAILWAY TRACK omouir Theodore Bodde, Rochester, N. Y., assignor to General Railway Signal Company, Rochester, N. Y.

Application May 15, 1931, Serial No. 537,667

11 Claims.

This invention relates to track circuits for railway signalling systems.

One purpose and feature of the present invention resides in the use of a relay of the tractive armature type for track circuits of the alternating current type, and consists in the use of a rectifier or electric current valve for improving the eificiency of such a relay and for reducing the vibration of the soft iron armature due to the Another feature of the present invention resides in the em ployment of a resistance in multiple with the winding of such a relay, which winding is in practice extremely highly inductive, whereby if a 15 single wave rectifier is used with such relay the impedance of the relay and its multiple resistance to the flow of the pulsating current produced by such rectifier will be materially reduced.

Other objects, purposes and characteristic features of the invention will in part be obvious from the accompanying drawing and will in part be more specifically pointed out hereinafter.

In describing the invention in detail reference will be made to the accompanying drawing, in

. which:--

Fig. 1 shows an alternating current track circuit of the usual construction, except that instead of using the usual form of alternating current track relay, a relay of the tractive soft iron ar mature type having a rectifier in multiple is employed therewith;

Fig. 2 shows a modified form of track circuit in which a transformer isolates the track relay from the track rails;

Fig. 3 shows a further modified track circuit in that the relay is bridged by a non-inductive r sistance and its energizing circuit includes a rectifier in series therewith; and I Fig. 4 is an arrangement similar to that shown in Fig. 3 except that the rectifier is locatedat the opposite end of the track circuit and the alternating current source is located at the relay end of the track circuit.

Referring to Fig. 1 of the drawing, the track rails l have been shown divided into blocks by insulating joints 2 to provide the usual insulated track section, over which traffic preferably moves from left to right as indicated by the" arrow. Across the exit end of this insulated section or locl; is connected a source of alternating current :AC through the medium of the transformer 3, and having the usual series resistance 4 included in its secondary circuit, and across the rails at the .55 entrance end of the block is connected a track relay T which has its winding bridged by a rectifier R It is thus seen that during that part of an alternating current cycle when the potential is from left to right across the track relay T that the current will find an easy path through the recti fier R but that during the other wave of this alternating current cycle the current cannot flow through the rectifier R by reason of its valve action and the current will find its easiestand lowest resistance path to be through the winding of the track relay T The advantage of this construction is due to the double function of the rectifier R in permitting current to be shunted from the relay duringv one wave of an alternating current cycle and not during the other wave of such cycle, and. further in providing a path for local current to flow duet-o the energy built up in the magnetic circuit of the track relay T In other words, when .current flows from right to left through the track relay T it builds up a magnetic field of a predetermined magnitude, and this magnetic field will not die down appreciably during the next wave of an alternating current cycle, because a slight dying down of the flux in the track relay T will produce a localcurrent flowing through the rectifier R which current will maintain the flux, so to sp'eak. f l

From this considerationof the arrangement shown in Fig. 1 it is apparentthat. the first cycle of alternating current will build up a'predetermined current value in the track relay T and that during the wave of this cycle when current readily flows through the rectifier R the current in the track relay T will not die appreciably, because the local current of the relay T through the rectifier R maintains the magnetic flux substantially at the acquired value. parent that for each successive cycle. of alternating current the flux density in the track relay T as well as the current flowing in the winding T will increase until it has reached its maximum value. It is thus seenthat the rectifierR serves two distinct purposes, first shunts the relay T for current flowing in .one direction, and second permits the current flowing throughthetrack relay for the other wave of i the. cycle-to be' maintained through a local circuit including the rectifier R I V Fig. 2 shows a track circuit exactly the same, as that shown in Fig. l exceptfor the inclusion of the shielding transformer 5T for isolating and. insulating the track relay'from'the track rails. This employment of a shielding transformer is resorted to in order to protect the rectifierh.

It isalso apfrom lighting disturbances and other foreign currents and potentials. Since many of the elements of the system shown in Fig. 2 are the same as those shown in Fig. 1 they have been assigned like reference characters or like reference characters having distinctive exponents.

The operation of either the circuit shown in Fig. 1 0r Fig. 2 is the same as the conventionally closed track circuit, in that a train entering the section between the insulated joints 2 shunts the secondary of the transformer 3 through the rails 1 which are bridged by the wheels and axles of the train, thereby practically deenergizing the associated relays T or T The resistance 4 is includeclin the energizing circuit to prevent the building up of an undue amount of current in the transformer 3 during such a short circuit thereon.

' It might also bepointed out that in the circuit shown in Fig. 1 the possibility of the relay T being falsely energized by the presence of foreign direct current energy on the track rails is reduced by the shunting action effected by the rectifier R on a definite polarity of such energy. This possibility, however, is not eliminated in the event of the application of the reverse polarity of such foreign energy, but is accomplished in the arrangement shown in Fig. 2 by the shielding of all direct current energy by the transformer ST In the modified form of the invention illustrated in Fig. 3 of the drawing, therectifier R is connected in series with the track relay T but the track relay T is shunted by a non-inductive resistance 5, the entire relay means including the relay T proper, the shunting resistance 5 and the rectifier R are isolated from the track rails by a shielding transformer 8T In this form of the invention the rectifier R permits current to flow from the secondary winding of the transformer ST only during one wave of an alternating current cycle, namely in the direction of the arrow of the legend'signifying this rectifien' This wave of current flow from this transformer for each cycle of alternating current in the direction of the arrow will divide inversely in accordance with the impedance of the coil T and the noninductive resistance 5, so that for the first wave a large part of the current will flow throughthe non-inductive resistance 5.

It should, however, be noted that during the opposite wave of a cycle of alternating current (when no current is permitted to flow by reason of the rectifier R the current in the track relay '1 due to the preceding wave is maintained in a local circuit including the winding T and the resistance 5 in series. Thus, the second cycle wave of current from the transformer ST passing through the rectifier R will be cumulative V with 'the current already fiowing in this track relay T so that for each successive cycle the cur rent in the track relay T is increased, it being maintained between the cycles, through a local circuit including the resistance 5 until the current in the track relay T has reached its maximum value. It will be maintained at this maximum value until the track rails are shunted by a moving train, which will of course deene'rgize the transformer ST and in turn the track,

. relay T In this connectionit may be pointed out that it has been foundin practice for the track relay T when connected in series with a rectifiersuch as R to require substantially only one-eighth of the voltage to pick it up if the'shunting resistance.

5 is employed than when such shunting resista ce 5 is omitted. In other words, the unit comprising the track relay T and the resistance 5 in multiple constitute adevice readily responsive to a pulsating current but not readily responsive to alternating current; and the rectifier R is employed to change the alternating current transmitted through the trackcircuit to a pulsating current.

The arrangement shown in Fig. 4 is very similar to that shown in Fig. 3, but is quite different in its functioning in that the alternating current source is at the track relay end of the track circuit, and the rectifier is at the opposite end of the track circuit in Fig.4, whereas in Fig. 3 the recti 'fier is'lo'cated at the track relay end and the alternating current source is located at the opposite end of the track circuit. Also, attention is directed to the fact that the series resistance 4 is entirely omitted from the track circuit in Fig. 4, this series resistance beingunnecessary because the track relay I is included in series with the secondary winding of the transformer 3 thereby preventing the entire short-circuiting of the alternating current source by wheels and axles of a passing train. 7

As already pointed out, a track relay of the soft iron tractive type is of very high impedance, and requires substantially eight times as much voltage to pick up such relay if not shunted by a resistance 5 than when so shunted, assuming of course that pulsating current is used. Therefore, employing that same reasoning, a relay of high inductance, when shunted by a non-inductive resistance such as resistance 5 will respond to pulsating current much more easily than it will to alternating current, this because the resistance unit 5 when alternating current is applied to the relay '1 does nothing but shunt part of the current away from the track relay T fore apparent that the track relay T will readily pick up due to pulsating current derived from the transformer 3 and flowing through the track circuit and the rectifier R but that as soon as It is therethe rectifier R is shunted by a train, which prevents functioning of this rectifier Rf, the track relay T will be supplied with alternating current energy. This alternating current fiows largely through the shunting resistance 5 and through the wheels and axles of the train thereby impressing insufiicient potential across the resistance 5 and track relay T to effect picking up of the soft iron armature of the track relay T It is thus seen that the arrangement shown in Fig. 4 constitutes a track circuit in which the of theenergizing circuit as by a train prevents its changing the current from alternating current to pulsatingcurrent and consequently effects derenergization of this relay unit which is designed to be readily responsive to pulsating current only.

Having thus shown severalyspecific embodiments of my invention it is desired to be understood that these various embodiments have not been illustrated forthe purpose of showing the scope'of the invention nor the precise structure to be employed in practicing the invention, but

have been selected for the purpose of facilitating a description of the underlying principles of the invention and the manner in which it may be applied in practicing the invention and various additions and modifications may be made to adapt the invention to the particular problem encountered in practicing the same, all without departing from the spirit or scope of the invention, except as demanded by the scope of the following claims.

What I claim as new is:-

1. In a track circuit having a section of railway track electrically insulated from the remaining track, an alternating current electrical circuit including the rails of said section and a device responsive only to uni-directional electrical current, and an asymmetric unit arranged to electrically shunt said device.

2. In a track circuit having a section of railway track electrically insulated from the remaining track, an electrical circuit including the rails of said section in series and having a source of alternating current and a highly inductive device responsive to uni-directional current connected in series across the track rails at one end of said section, and means connected across the track rails at the other end of said section for changing the alternating current derived from said source to uni-directional current and a non-inductive resistor connected to electrically shunt said current responsive device.

3. In a track circuit having a section of railway track electrically insulated from the remaining track, a source of alternating currentconnected at one end of said section to energize said rails, an asymmetric unit in series with a device responsive to uni-directional current connected at the other end of said section to receive said energy and a non-inductive resistor connected to electrically shunt said current responsive device.

4. A track circuit including a source of alternating current and the rails of said track in series, an electro-responsive device having means associated therewith to asymmetrically impede the alternations of current from said source of current and a shunt path for said electro-responsive device arranged to maintain the less impeded alternation of said current.

5. In combination, a section of railway track electrically insulated from the remaining track, a source of alternating current connected to the rails at one end of said section of track, a tractive type relay connected to the rails at the other end of said section of track and means to asymmetrically conduct alternating current connected in multiple with said relay.

6. In combination, a section of railway track electrically insulated from the remaining track,

a transformer having a secondary winding connected to the rails at one end of said section of track, a source of alternating current connected to a primary winding of said transformer, a second transformer having a primary winding connected to the rails of said section of track at the other end thereof, a tractive type relay connected to a secondary winding of said second transformer and means to asymmetrically conduct alternating current connected in multiple with said relay.

'7. In combination, a section of railway track electrically insulated from the remaining track, a transformer having a secondary winding connected to the rails at the exit end of said section of track, a source of alternating current connected to a primary winding of said transformer, a second transformer having a primary winding connected to the rails of said section of track'at the entrance end thereof, an asymmetric unit and a tractive type relay connected in series to a secondary winding of said second transformer and a non-inductive electrical resistor connected in multiple with said relay.

8. In combination, a section of railway track electrically insulated from the remaining track, a transformer, a source of alternating current connected to a primary winding of said transformer, a tractive type relay connected in series with a secondary Winding of said transformer to the rails at one end of said section of track, a non-inductive electrical resistor connected in multiple with said relay and an asymmetric unit connected to the rails at the other end of said section of track.

9. In combination, a section of railway track, a source of alternating current and a direct current track relay connected across the rails at one end of the section, an impedance interposed between said source and one rail, and a rectifier connected across the rails at the other end of the section.

10. In combination, a section of railway track, a source of alternating current and a direct current track relay connected across the rails at one end of the section, a resistance interposed between said source and one rail, and a rectifier connected across the rails at the other end of the section.

11. In combination, a section of railway track, a source of alternating current and a direct current track relay connected across the rails at one end of the section, a resistance bridged across rails at the other end of the section.

THEODORE BODDE. 

